Implement IME-related methods of SctkWinitWindow for apps using single-instance feature

- At least, following apps are using `single-instance` feature:
  - cosmic-launcher
  - cosmic-app-library
- Once libcosmic text widgets supported the IME, these apps start hitting following methods of SctkWinitWindow which is `todo!()` and will crash at startup:
  - `set_ime_cursor_area()`
  - `set_ime_allowed()`
  - `set_ime_purpose()`
- So, this PR implements these method utilizing following wayland protocols.
  - zwp_text_input_v3
  - zwp_text_input_manager_v3

winit/src/platform_specific/wayland/handlers/mod.rs

@@ -7,6 +7,7 @@ pub mod seat;
 pub mod session_lock;
 pub mod shell;
 pub mod subcompositor;
+pub mod text_input;
 pub mod toplevel;
 pub mod wp_fractional_scaling;
 pub mod wp_viewporter;

winit/src/platform_specific/wayland/handlers/seat/seat.rs

@@ -8,6 +8,7 @@ use cctk::sctk::{
     seat::{pointer::ThemeSpec, SeatHandler},
 };
 use iced_runtime::keyboard::Modifiers;
+use std::sync::Arc;
 
 impl SeatHandler for SctkState {
     fn seat_state(&mut self) -> &mut cctk::sctk::seat::SeatState {
@@ -141,6 +142,16 @@ impl SeatHandler for SctkState {
             }
             _ => unimplemented!(),
         }
+
+        if let Some(text_input_manager) = self
+            .text_input
+            .is_none()
+            .then_some(self.text_input_manager.as_ref())
+            .flatten()
+        {
+            self.text_input =
+                Some(Arc::new((text_input_manager).get_text_input(&seat, &qh)));
+        }
     }
 
     fn remove_capability(
@@ -193,6 +204,10 @@ impl SeatHandler for SctkState {
             }
             _ => unimplemented!(),
         }
+
+        if let Some(text_input) = self.text_input.take() {
+            text_input.destroy();
+        }
     }
 
     fn remove_seat(

winit/src/platform_specific/wayland/handlers/text_input.rs

@@ -0,0 +1,130 @@
+use cctk::sctk::globals::GlobalData;
+use cctk::sctk::reexports::client::{Connection, Proxy, QueueHandle};
+
+use cctk::sctk::reexports::client::delegate_dispatch;
+use cctk::sctk::reexports::client::Dispatch;
+use cctk::sctk::reexports::protocols::wp::text_input::zv3::client::zwp_text_input_manager_v3::ZwpTextInputManagerV3;
+use cctk::sctk::reexports::protocols::wp::text_input::zv3::client::zwp_text_input_v3::Event as TextInputEvent;
+use cctk::sctk::reexports::protocols::wp::text_input::zv3::client::zwp_text_input_v3::ZwpTextInputV3;
+use cctk::sctk::registry::RegistryState;
+use wayland_client::protocol::wl_seat::WlSeat;
+use winit::event::{Ime, WindowEvent};
+use winit::window::WindowId;
+
+use crate::event_loop::state::SctkState;
+use crate::sctk_event::SctkEvent;
+
+pub struct Preedit {
+    text: String,
+    cursor_range: Option<(usize, usize)>,
+}
+
+pub struct TextInputManager {
+    manager: ZwpTextInputManagerV3,
+}
+
+impl TextInputManager {
+    pub fn try_new<D>(
+        registry: &RegistryState,
+        qh: &QueueHandle<D>,
+    ) -> Option<Self>
+    where
+        D: Dispatch<ZwpTextInputManagerV3, GlobalData> + 'static,
+    {
+        let manager = registry
+            .bind_one::<ZwpTextInputManagerV3, _, _>(qh, 1..=1, GlobalData)
+            .ok()?;
+        Some(Self { manager })
+    }
+
+    pub fn get_text_input(
+        &self,
+        seat: &WlSeat,
+        qh: &QueueHandle<SctkState>,
+    ) -> ZwpTextInputV3 {
+        self.manager.get_text_input(&seat, &qh, ())
+    }
+}
+
+impl Dispatch<ZwpTextInputManagerV3, GlobalData, SctkState>
+    for TextInputManager
+{
+    fn event(
+        _state: &mut SctkState,
+        _proxy: &ZwpTextInputManagerV3,
+        _event: <ZwpTextInputManagerV3 as Proxy>::Event,
+        _data: &GlobalData,
+        _conn: &Connection,
+        _qhandle: &QueueHandle<SctkState>,
+    ) {
+    }
+}
+
+impl Dispatch<ZwpTextInputV3, (), SctkState> for TextInputManager {
+    fn event(
+        state: &mut SctkState,
+        _text_input: &ZwpTextInputV3,
+        event: <ZwpTextInputV3 as Proxy>::Event,
+        _data: &(),
+        _conn: &Connection,
+        _qhandle: &QueueHandle<SctkState>,
+    ) {
+        let kbd_focus =
+            match state.seats.iter_mut().find_map(|s| s.kbd_focus.clone()) {
+                Some(surface) => surface,
+                None => return,
+            };
+        match event {
+            TextInputEvent::PreeditString {
+                text,
+                cursor_begin,
+                cursor_end,
+            } => {
+                let text = text.unwrap_or_default();
+                let cursor_begin = usize::try_from(cursor_begin)
+                    .ok()
+                    .and_then(|idx| text.is_char_boundary(idx).then_some(idx));
+                let cursor_end = usize::try_from(cursor_end)
+                    .ok()
+                    .and_then(|idx| text.is_char_boundary(idx).then_some(idx));
+                let cursor_range =
+                    cursor_begin.map(|b| (b, cursor_end.unwrap_or(b)));
+                state.preedit = Some(Preedit { text, cursor_range });
+            }
+            TextInputEvent::CommitString { text } => {
+                state.preedit = None;
+                state.pending_commit = text;
+            }
+            TextInputEvent::Done { .. } => {
+                let id = WindowId::from_raw(kbd_focus.id().as_ptr() as usize);
+                state.sctk_events.push(SctkEvent::Winit(
+                    id,
+                    WindowEvent::Ime(Ime::Preedit(String::new(), None)),
+                ));
+
+                // Commit string
+                if let Some(text) = state.pending_commit.take() {
+                    state.sctk_events.push(SctkEvent::Winit(
+                        id,
+                        WindowEvent::Ime(Ime::Commit(text)),
+                    ));
+                }
+
+                // Update preedit string
+                if let Some(preedit) = state.preedit.take() {
+                    state.sctk_events.push(SctkEvent::Winit(
+                        id,
+                        WindowEvent::Ime(Ime::Preedit(
+                            preedit.text,
+                            preedit.cursor_range,
+                        )),
+                    ));
+                }
+            }
+            _ => {}
+        }
+    }
+}
+
+delegate_dispatch!(SctkState: [ZwpTextInputManagerV3: GlobalData] => TextInputManager);
+delegate_dispatch!(SctkState: [ZwpTextInputV3: ()] => TextInputManager);